Passengers aboard the Ocean Adventures catamaran were not going to need a bigger boat, it turned out, because what looked like the fin of a gigantic shark belonged to a blue whale. The unusual sighting on Sunday off Dana Point, Calif., was thanks to a large blue whale that turned on its side, allowing a portion of its tail fluke to slice through the water for an extended period alongside the vessel.

Donna Kalez, manager of Dana Wharf Whale Watching, said her captains have seen blue whales quickly roll over, briefly revealing a section of their fluke in this manner. But in this instance the whale remained in a sideways position for an extended period, allowing its tail fin to slice through the water looking strikingly like a fin belong to a certain member of the 1970s thriller, “Jaws.”

Viewers of the video can hear the clicking of camera shutters during this event, and one passenger can even be heard saying, “He’s doing his ‘Jaws’ impersonation.”

Endangered blue whales are the largest creatures on the planet, reaching lengths of nearly 100 feet and weights of up to 150 tons. About 2,000 of blue whales spend the summer and early fall off the West Coast, gorging on shrimp-like krill.

Blue whales have been spotted off Dana Point, in Orange County, every day for more than a month.

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